Windmills have been used for many generations for the purpose of pumping water from the ground and for generating electricity. A basic advantage of the windmill is that it uses the power of atmospheric wind to rotate a wheel having radially extending blades. This rotary movement may be converted into various useful purposes. For example, wind turbines in the form of propellers mounted on towers have been placed in areas where steady winds are prevalent and the wind turbines are used to generate electricity.
The blades of the conventional wind turbines are very large and made of expensive rigid material and are constructed to have the blades extend radially from a central hub, with no extra support at the outer tips of the blades. The conventional wind turbine blades rotate at a high rate of revolution and must withstand the centrifugal forces generated by the fast revolution of the blades, the cantilever bending forces applied to the blades by the wind, and the twisting forces applied to the pitched surfaces of the blades. Since the outer portions of the blades move at a very high velocity and are engaged by strong winds, the larger blades require the blades to be strong, and the stronger they are the more expensive they become. Thus, there is a practical limit as to the length and width of the blades.
Some of the prior art wind turbines are constructed with an outer rim that extends circumferentially about the turbine wheel and the blades are supported at their outer ends by the circumferential rim. Rubber tires are placed in positions to engage the outer rim so as to rotate the rubber tires, with the driven rubber tires rotating the rotors of generators. Thus, the rotation of the wind turbine is used to generate electricity.
Prior art wind turbines are mounted on upright towers and the towers are supported at their bases by mounting the towers in the earth or on some other stable platform. When the wind turbine is in operation with an oncoming brisk wind engaging the angled blades of the turbine wheel, a significant longitudinal force is transmitted from the blades of the turbine wheel to the upper portion of the tower, tending to tip the tower. This horizontal tipping force usually is significantly greater than the circumferential wind force engaging the angled surfaces of the blades of the turbine wheel and causing the rotation of the turbine wheel. This longitudinal force requires the tower for a wind turbine to be very strong to avoid tipping over.
While wind turbines have found use in open land areas where steady winds are prevalent, the land areas most suitable for catching the wind on wind turbine propeller blades usually are remote from the areas of greatest need of electrical power. Therefore, there is a requirement that electrical power be transmitted through conductive cables for long distances to the areas of need.
Winds generated over large bodies of water, particularly over an ocean, are not confronted with mountains, buildings, and the vegetation of the land masses that tend to slow the velocity of winds. The turbulence of wind usually is less over water than over land. This may be because there is a greater temperature variance between different altitudes over land than over a body of water, apparently because sunlight is absorbed further into water than into land, and for comparable conditions, the surfaces of land become warmer and radiate more heat than the surfaces of water.
Also, some of the largest cities of the world are positioned adjacent large bodies of water such as adjacent oceans and seas where wind velocities are not slowed and are less turbulent near the water surface and are more predictable.
Another advantage of wind turbines placed on bodies of water is that the less turbulent winds at the surface of the water allow the turbine wheel to be supported lower, closer to the surface of the water. This tends to reduce the expense of having a tall tower as usually required for land mounted wind turbines.
Accordingly, it would be desirable to locate wind turbines on bodies of water spaced relatively close to a land mass where there is a need for electricity. Also, it would be desirable to produce wind turbines with a means for reducing the longitudinal force applied by the turbine wheel to the tower or other vertical support of the wind turbine. Also, it would be desirable that a wind turbine supported on a body of water be able to turn into the oncoming wind when the wind changes directions, and that the perimeter of the turbine wheel be used to generate electricity.
Also, it would be desirable to produce and use a wind turbine or other rotary device that operates an electrical generator with a reduction in the drag and friction in the course of producing electricity, and to permit a wider range of rates of rotation of the turbine wheel while producing electricity. The wind turbine may include an outer perimeter rim that may be used for both stabilizing and supporting the sail wings or propellers of the wind turbine wheel and for forming a rotor for a stator that, together, function as an electrical generator.